Max Planck Research Magazin features Jens Bardarson
What do soccer and quantum mechanics have in common? Both have surprising twists in store that are difficult to predict. Soccer, however, at least follows some rules that are more or less reliable. As a striker, Jens Hjörleifur Bárdarson controls the ball; as a physicist, he masters the rules of the quantum universe. The 35-year-old researcher at the Max Planck Institute for the Physics of Complex Systems in Dresden studies atomic particles, which display many a tricky move.
Many-Body Localization Characterized from a One-Particle Perspective
We show that the one-particle density matrix $\rho$ can be used to characterize the interaction-driven many-body localization transition in closed fermionic systems. The natural orbitals (the eigenstates of $\rho$ ) are localized in the many-body localized phase and spread out when one enters the delocalized phase, while the occupation spectrum (the set of eigenvalues of $\rho$ ) reveals the distinctive Fock-space structure of the many-body eigenstates, exhibiting a step-like discontinuity in the localized phase. The associated one-particle occupation entropy is small in the localized phase and large in the delocalized phase, with diverging fluctuations at the transition. We analyze the inverse participation ratio of the natural orbitals and find that it is independent of system size in the localized phase.
S. Bera, H. Schomerus, F. Heidrich-Meisner, and J. H. Bardarson
Phys. Rev. Lett. 115, 046603 (2015)
Avalanche outbreaks emerging in cooperative contagions
During human history the world has witnessed an immense loss of lives caused by infectious diseases. The number of casualties becomes even more concerning the cases of syndemic diseases (cooperative contagion), when two or more diseases co-infect individuals in a host population. For example the 1918 Spanish pandemic killed 20-40 million people mainly because of secondary bacterial infections. Contemporary syndemics that pose a major threat to public health include coinfection of HIV, Hepatitis B, C and TB. Here we modeled pathogens that spread and interact on networks, i.e. contact networks between individuals. These interactions can be cooperative and effectively change the way syndemic diseases spread and proliferate in populations. We showed that cooperation of the spreading infections can cause abrupt unexpected outbreaks at smaller epidemic thresholds, while underlying network can amplify or suppress this effect.
W. Cai, L. Chen, F. Ghanbarnejad, and P. Grassberger
Nature Physics (2015)
Johannes Knolle erhält den Dissertationspreis der Sektion kondensierte Materie der DPG
Ziel des Preises ist die Anerkennung herausragender wissenschaftlicher Arbeit und deren exzellenter Darstellung in einem Vortrag. Zur Verleihung an Johannes Knolle, der am MPIPKS in der Abteilung Kondensierte Materie promovierte, schreibt die Jury: Die numerisch exakte Evaluierung des dynamischen Strukturfaktors einer fraktionierten Quantenspinflüssigkeit stellt einen Durchbruch für unser Verständnis topologischer Magnete in zwei Dimensionen dar. Sie ist von Bedeutung für die Suche nach topologischen Materialien, für die Methodik der Vielteilchentheorie, sowie als Beispiel eines lokalen Quantenquenches.
Dr. Frank Pollmann erhält den Walter-Schottky-Preis 2014 für seine Arbeit zum Konzept symmetriegeschützter topologischer Zustände. Das Preiskomittee schreibt: In den letzten Jahren hat das Feld topologischer Quantenzustände weltweit eine rasante Entwicklung genommen. Durch wegweisende Arbeiten haben Frank Pollmann und Andreas Schnyder mit ihren Ko-Autoren maßgeblich dazu beigetragen, die Vielfalt topologischer Systeme und Phänomene zu erkennen und an Hand von Symmetrieüberlegungen zu systematisieren. Andreas Schnyder gelang die Klassifizierung topologischer Isolatoren, Supraleiter und Halbmetalle. Frank Pollmann hat das Konzept symmetriegeschützter topologischer Ordnung entwickelt.
New research group 'Ultrafast laser-matter interaction'
The new group is headed by Dr. Alexandra Landsman and studies the creation of ultrafast flashes of light and the interaction of this ultrafast light with matter using a variety of numerical and analytic methods, ranging from the solution of the Schrodinger equation to semi-classical approaches to techniques from nonlinear dynamical systems.
Scaling and Regeneration of Self-Organized Patterns
Biological patterns generated during development and regeneration often scale with organism size. Some organisms, e.g., flatworms, can regenerate a rescaled body plan from tissue fragments of varying sizes. Inspired by these examples, we introduce a generalization of Turing patterns that is self-organized and self-scaling. A feedback loop involving diffusing expander molecules regulates the reaction rates of a Turing system, thereby adjusting pattern length scales proportional to system size. Our model captures essential features of body plan regeneration in flatworms as observed in experiments.
S. Werner, T. Stückemann, M. B. Amigo, J. C. Rink, F. Jülicher, B. M. Friedrich
Phys. Rev. Lett. 114, 138101 (2015)
The mechanical behaviour of cells is largely controlled by a structure that is fundamentally out of thermodynamic equilibrium: a network of crosslinked filaments subjected to the action of energy-transducing molecular motors. The study of this kind of active system was absent from conventional physics and there was a need for both new theories and new experiments. The field that has emerged in recent years to fill this gap is underpinned by a theory that takes into account the transduction of chemical energy on the molecular scale. This formalism has advanced our understanding of living systems, but it has also had an impact on research in physics per se. Here, we describe this developing field, its relevance to biology, the novelty it conveys to other areas of physics and some of the challenges in store for the future of active gel physics.
J. Prost, F. Jülicher, J-F. Joanny
Nature Physics 11, 111-117 (2015)
Random walk is a fundamental concept with applications ranging from quantum physics to econometrics. Remarkably, one specific model of random walks appears to be ubiquitous across many fields as a tool to analyze transport phenomena in which the dispersal process is faster than dictated by Brownian diffusion. The Lévy-walk model combines two key features, the ability to generate anomalously fast diffusion and a finite velocity of a random walker. Recent results in optics, Hamiltonian chaos, cold atom dynamics, biophysics, and behavioral science demonstrate that this particular type of random walk provides significant insight into complex transport phenomena. This review gives a self-consistent introduction to Lévy walks, surveys their existing applications, including latest advances, and outlines further perspectives.
V. Zaburdaev, S. Denisov, and J. Klafter
Rev. Mod. Phys. 87, 483 (2015)
During embryonic development, temporal and spatial cues are coordinated to generate a segmented body axis. In sequentially segmenting animals, the rhythm of segmentation is reported to be controlled by the time scale of genetic oscillations that periodically trigger new segment formation. However, we present real-time measurements of genetic oscillations in zebrafish embryos showing that their time scale is not sufficient to explain the temporal period of segmentation. A second time scale, the rate of tissue shortening, contributes to the period of segmentation through a Doppler effect. This contribution is modulated by a gradual change in the oscillation profile across the tissue. We conclude that the rhythm of segmentation is an emergent property controlled by the time scale of genetic oscillations, the change of oscillation profile, and tissue shortening.
Daniele Soroldoni, David J. Jörg, Luis G. Morelli, David L. Richmond, Johannes Schindelin, Frank Jülicher, Andrew C. Oates
Science, 11 July 2014